1. Field of the Invention
The present invention relates generally to phase change inks. Still further, the present invention relates to processes of using phase change inks in printing devices. Additionally, the present invention relates to processes of using polyethylene wax as a transparent overcoat layer on a printed substrate to provide improved document feed capability from photocopiers.
2. Description of the Relevant Art
In general, phase change inks (sometimes referred to as “hot melt inks”) are in the solid phase at ambient temperature, but exist in the liquid phase at the elevated operating temperature of an ink jet printing device. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the printing media, they quickly solidify to form a predetermined pattern of solidified ink drops. Phase change inks have also been investigated for use in other printing technologies such as gravure printing as referenced in U.S. Pat. No. 5,496,879 and German patent publications DE 4205636AL and DE 4205713AL assigned to Siegwerk Farbenfabrik Keller, Dr. Rung and Co.
Phase change inks for color printing generally comprise a phase change ink carrier composition, which is combined with a phase change ink compatible colorant. Preferably, a colored phase change ink will be formed by combining the above-described ink carrier composition with compatible subtractive primary colorants. The subtractive primary colored phase change inks can comprise four component dyes, namely, cyan, magenta, yellow and black. U.S. Pat. Nos. 4,889,506; 4,889,761; and 5,372,852 teach that the subtractive primary colorants employed typically may comprise dyes from the classes of Color Index (C.I.) Solvent Dyes, Disperse Dyes, modified Acid and Direct Dyes, and a limited number of Basic Dyes. The colorants can also include pigments as exemplified in U.S. Pat. No. 5,221,335, assigned to Coates Electrographics LTD. U.S. patent application Ser. No. 08/381,610, filed Jan. 30, 1995, and assigned to Tektronix, Inc. (now U.S. Pat. No. 5,621,022), is directed to the use of a specific class of polymeric dyes in phase change ink compositions.
Phase change inks are desirable for ink jet printers since they remain in a solid phase at room temperature during shipping, long-term storage, and the like. Also, the problems associated with nozzle clogging due to ink evaporation are largely eliminated, thereby improving the reliability of ink jet printing. Furthermore, ink droplets can be applied directly onto a printing medium (substrate) and be configured to solidify immediately upon contact with the substrate. Migration of ink along the printing medium can thus be prevented and dot quality improved.
In addition to the above-referenced U.S. patents, many other patents describe materials for use in phase change ink jet inks. Some representative examples include U.S. Pat. Nos. 3,653,932; 4,390,369; 4,484,948; 4,684,956; 4,851,045; 4,889,560; 5,006,170; and 5,151,120; as well as EP Application Nos. 0187352 and 0206286. These materials can include paraffins, microcrystalline waxes, polyethylene waxes, ester waxes, fatty acids and other waxy materials, fatty amide-containing materials, sulfonamide materials, resinous materials made from different natural sources (tall oil rosins and rosin esters are an example) and many synthetic resins, oligomers, polymers and co-polymers.
Separately, PCT Patent Application WO 94/14902, which was published on Jul. 7, 1994 and is assigned to Coates Brothers PLC, teaches a hot melt ink containing a colorant and, as a vehicle for the hot melt ink, an oligourethane having a melting point of at least 65° C. and obtained by reacting an aliphatic or aromatic diisocyanate with at least a stoichiometric amount of either: (i) a monohydric alcohol component; or (ii) a monohydric alcohol component followed by another different monohydric alcohol component; or (iii) a monohydric alcohol component, followed by a dihydric alcohol component, followed by a monohydric alcohol component.
This PCT patent application defines the monohydric alcohol component as either a monohydric aliphatic alcohol (e.g. C1 to C22 alcohols), an etherified dihydric aliphatic alcohol (e.g. propylene glycol methyl ether (PGME), dipropylene glycol methyl ether (DPGME), ethylene glycol butyl ether (EGBE), diethylene glycol butyl ether (DPGBE), tripropylene glycol butyl ether (TPGBE) and propylene glycol phenyl ether (PPL)); esterified dihydric aliphatic alcohol (e.g. the esterifying acid may be an ethylenically unsaturated acid (such as acrylic acid or methacrylic acid), thereby introducing ethylenic unsaturation into the oligourethane and rendering it suitable for eventual further additional polymerization (curing) after having been applied to a substrate by hot melt printing), or dihydric polyalkylene glycol. This PCT Application further defines the dihydric alcohol component as a dihydric aliphatic alcohol or a dihydric polyalkylene glycol (e.g. ethylene glycol, polyethylene glycol (PEG 1500), polypropylene glycol (PPG 750, 1000 and 1500), trimethylene glycol, dipropylene glycol, methylpropanediol and 1,6-hexanediol).
Also, PCT Patent Application WO 94/04619, assigned to the General Electric Company, teaches the use of ionomeric materials in combination with image forming agents to form a hot melt ink jet ink. The ionomeric materials can include many different types of copolymeric or polymeric ionomers, including carboxyl-functional polyurethanes prepared from a diol or polyol and a hydroxyl acid. Many other carrier materials and colorants for the image forming agent of the invention are included in this PCT application.
Furthermore, U.S. patent application Ser. No. 08/672,815, (now U.S. Pat. No. 5,830,815) assigned to the Assignee of the present invention, teaches phase change carrier compositions that comprise the combination of a urethane resin with a urethane/urea resin that may optionally contain other ingredients such as mono-amides and polyethylene waxes.
However, there is still a need for new materials for novel and different applications of phase change carrier compositions and inks containing such carrier compositions. There is a also a need for low viscosity phase change carrier compositions and inks having non-polymeric resins and waxes designed for phase change ink jet and other forms of phase change ink printing. Such carrier compositions and inks being substantially transparent and having a reduced surface coefficient of friction as compared to presently known carrier compositions and inks. It would be advantageous if ink sticks which have an improved surface appearance and better release from molds and waste collection trays than previously known ink sticks could also be formed from such carrier compositions and inks. Additionally, it would be desirable if such phase change ink and carrier compositions include improved blocking performance of finished prints than has been previously known.